From: Kurt  Stephens <redmine@...>
Date: 2011-01-12T06:05:50+09:00
Subject: [ruby-core:34385] [Ruby 1.9-Feature#4264] General type coercion protocol for Ruby

Issue #4264 has been updated by Kurt  Stephens.


Below is the simple, extensible technique used in Oaklisp.
Give each Module a coercer Symbol.
Apply the target type's coercer to the object to be coercer.
Cost is two message sends.

class Module
  IDENTITY_PROC = lambda { | obj | obj }
  def coercer
    unless @coercer 
      @coercer = :"#{self.name}_coercer"
      define_method(@coercer, &IDENTITY_PROC)
    end
    @coercer
  end
end

class Object
  def as(mod)
    send(mod.coercer, self)
  end
end

#########################################

class String
  define_method(Float.coercer) { | obj | obj.to_f }
end

class Float
  define_method(String.coercer) { | obj | obj.to_s }
end

#########################################
require 'pp'

x = 1.23
pp [ x, String.coercer, x.as(String) ]
pp [ x, Float.coercer, x.as(Float) ]

x = "2.34"
pp [ x, String.coercer, x.as(String) ]
pp [ x, Float.coercer,  x.as(Float) ]


##########################

[1.23, :String_coercer, "1.23"]
[1.23, :Float_coercer, 1.23]
["2.34", :String_coercer, "2.34"]
["2.34", :Float_coercer, 2.34]


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http://redmine.ruby-lang.org/issues/show/4264

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